Process and catalyst for cracking of ethers and alcohols

ABSTRACT

A process for the production of olefins from at least one of an alcohol and ether, the process including: contacting at least one alcohol or ether with a hydrofluoric acid-treated amorphous synthetic alumina-silica catalyst under decomposition conditions to produce an olefin. Also disclosed is a process for the production of isobutylene from methyl tertiary butyl ether, the process including: feeding methyl tertiary butyl ether (MTBE) to a reactor having at least one reaction zone containing a hydrofluoric acid-treated amorphous synthetic alumina-silica catalyst; contacting the MTBE with the hydrofluoric acid-treated amorphous synthetic alumina-silica catalyst under decomposition conditions to produce a reactor effluent comprising isobutylene, unreacted MTBE, heavies, and methanol; feeding the reactor effluent to a first distillation column; separating the isobutylene from the unreacted MTBE, heavies, and the methanol in the first distillation column to recover a first bottoms fraction comprising heavies, unreacted MTBE, and methanol and an isobutylene-rich overheads fraction.

CROSS-REFERENCE TO RELATED APPLICATION

This application, pursuant to 35 U.S.C. §120, claims benefit to U.S.application Ser. No. 13/450,669, now U.S. Pat. No. 8,829,260, whichpursuant to 35 U.S.C. §120, claims benefit to U.S. application Ser. No.12/260,729, now U.S. Pat. No. 8,395,008, which pursuant to 35 U.S.C.§119(e), claims priority to U.S. Provisional Application Ser. No.61/020,883, filed Jan. 14, 2008, U.S. Provisional Application Ser. No.61/022,119, filed Jan. 18, 2008, and U.S. Provisional Application Ser.No. 61/094,676, filed Sep. 5, 2008. Each of these applications isincorporated by reference in its entirety.

BACKGROUND OF DISCLOSURE

1. Field of the Disclosure

Embodiments disclosed herein relate generally to catalysts and processesfor the decomposition of ethers and alcohols to form olefins. Morespecifically, embodiments disclosed herein relate to hydrofluoric acidtreated amorphous synthetic alumina-silica catalysts useful for thedecomposition of ethers, such as alkyl tertiary-alkyl ethers, to formolefins, such as tertiary olefins.

2. Background

Ethers may be decomposed to corresponding olefins and alcohols in thepresence of an acid catalyst. For example, alkyl tertiary-alkyl ethers,such as methyl tertiary-butyl ether (MTBE) or tertiary-amyl methyl ether(TAME) may be cracked to tertiary olefins and corresponding alcoholsover an acidic solid catalyst. The resulting olefin products,isobutylene and isoamylenes, are important raw materials for variousapplications. Isobutylene, for example, is a raw material for productionof synthetic rubber. Isoamylene is a raw material for variousspecialized applications, such as herbicides, flavors, fragrances, and acopolymerization agent, among others.

One major difficulty encountered in the catalytic cracking of alkyltertiary-alkyl ethers is a relatively short catalyst cycle length,generally caused by polymer deposition on the catalyst due to the highlyreactive nature of the tertiary olefins. Additionally, a very smallamount of dienes or diene-precursors may be detrimental to catalystlongevity. Thus, dienes and diene-precursors in feed streams aretypically removed by hydrogenation, distillation, or both.

Various natural clays are acidic materials that can serve as catalystsfor acid catalyzed chemical reactions, such as the cracking of alkyltertiary-alkyl ethers. Clays are naturally occurring crystallinephyllosilicate minerals (mostly aluminosilicates) with variousimpurities. Aluminum, magnesium, calcium, sodium, and the like, areimportant cationic components of layered silicate minerals. When thesecationic species, especially mono and divalent cations, are removed byproper chemical means, Brönstead acidic sites are introduced to the claymaterials, and they can serve as acidic catalysts for various chemicalreactions.

Many clays have layered or ordered structures. For example, kaolin,montmorillonite, attapulgite, bentonite, beidellites, and other clayshave layered structures. When such clays are properly treated, theybecome quite acidic. As a means to increase catalytic active sites,pillars may be introduced between the clay layers in addition tocreating acidic sites. This pillaring technique multiplies the number ofcatalytic acidic sites.

Both acidic clays and synthetic aluminosilicates have been used as amatrix for producing fluid catalytic cracking (FCC) catalysts. Calcinedkaolin has been utilized as a raw material in the synthesis of Y-zeolitein microsphere form. Additionally, dehydration of ethanol to ethyleneover mixed oxides of alumina-silica and alumina catalysts was studied byJ. Koubek et al., Proceedings of the 7^(th) International Congress onCatalysis, Part B, 853, 1980.

U.S. Pat. No. 4,398,051 discloses obtaining high purity tertiaryolefins, such as isobutylene, by decomposition of alkyl-tertiary-alkylethers over acidic catalysts. The catalyst used was an alumina compoundsupported on a carrier containing silicon dioxides. The alumina compoundon a support is decomposed by calcining at high temperatures (750-1000°C.). The carriers included silica, montmorillonite, kaolinite,attapulgite, silica-zirconia, and others. However, no data regardingcatalyst stability or catalyst deactivation is presented.

U.S. Pat. Nos. 5,043,518 and 4,691,073 disclose a process using claycatalysts for producing isoamylenes by cracking TAME over variousnatural clay catalysts, such as attapulgite clay, treated with anaqueous hydrofluoric acid (HF) solution. Benefits disclosed by treatingthe natural clays with HF include a higher activity and increasedcatalyst stability, which are measured in terms of cracking temperaturerequired to maintain 95% conversion of TAME. This type of clay is alsoan effective catalyst for the production of isobutylene from MTBE. Thesepatents also mention use of synthetic clays in passing, and do notpresent any data directed toward synthetic clays.

Commercially, attapulgite clay catalysts are sold as granules.Unfortunately, attapulgite clay catalysts do not have good physicalintegrity. Additionally, HF treatment further weakens the physicalintegrity, which is measured by attrition rate or crushing strength. Asa result, the HF treated attapulgite clays must be handled with care,and the catalyst life is typically no more than 6 months.

Other downfalls of HF treated attapulgite clays include disposal costs.Such catalysts must be treated or otherwise rendered inert prior todisposal, adding to the cost of producing tertiary olefins. Additionalcosts are encountered by the large amount of HF required for the claytreating process, increasing raw material costs and creating a largeamount of fluorinated waste solution. Although the HF treatedattapulgite generates a lot of waste materials, the service time anddeactivation are a significant improvement over untreated claycatalysts.

Another downside to use of HF treated clays includes increasedproduction of byproducts, such as dimethyl ether (DME). Because of thehigher catalytic activity of HF treated clays, they produce, in general,more DME than untreated clay catalysts. Catalyst deactivation typicallyresults in a lower conversion of alkyl tertiary-alkyl ethers, such thatthe cracking temperature is raised to maintain a steady conversion asthe catalyst deactivates. As treated attapulgite clay catalystsdeactivate at a slower rate than untreated catalyst, the slowertemperature ramping does not affect DME production as much as foruntreated clay catalysts. Decreased DME production is a desired benefitnot generally obtained with HF treated attapulgite clays.

U.S. Pat. No. 5,043,519 ('519) discloses a process for the production oftertiary olefins by decomposing alkyl tertiary-alkyl ethers in thepresence of a catalyst containing 0.1 to 1.5 weight percent alumina onsilica. As disclosed, at least 0.5 weight percent alumina is requiredfor slower catalyst deactivation, and addition of small quantities ofwater into the feed stream may suppress DME formation. Nevertheless, theexperimental results presented in Table 2 of the '519 patent shows morethan about 1800 ppm DME by weight in the product stream at about 75%MTBE conversion, and more than 4500 ppm DME at a slightly higherconversion of 76.8%.

U.S. Pat. Nos. 4,880,787, 4,871,446, 4,888,103, and 4,324,698 eachmention that amorphous silica-alumina catalysts are useful as crackingcatalysts. However, as noted in U.S. Pat. No. 4,880,787, the majorconventional cracking catalysts in use at that time (late 1980's, early1990's), the same time period as the aforementioned U.S. Pat. No.4,691,073, generally incorporated a large pore crystallinealuminosilicate. To the present inventor's knowledge, commercialsynthetic silica-alumina catalysts for cracking remain to this day to beof a crystalline nature.

Accordingly, there exists a need for improved catalysts for theproduction of tertiary olefins. Such improved catalysts are desired tohave one or more of an increased cycle length, good physical integrity,a low attrition rate, a high crushing strength, decreased productioncosts, and decreased disposal costs.

SUMMARY OF THE DISCLOSURE

In one aspect, embodiments disclosed herein relate to a process for theproduction of olefins from at least one of an alcohol and an ether, theprocess including: contacting at least one of an alcohol and an etherwith a hydrofluoric acid-treated amorphous synthetic alumina-silicacatalyst under decomposition conditions to produce an olefin.

In another aspect, embodiments disclosed herein relate to a process forthe production of isobutylene from methyl tertiary butyl ether, theprocess including: feeding methyl tertiary butyl ether (MTBE) to areactor having at least one reaction zone containing a hydrofluoricacid-treated amorphous synthetic alumina-silica catalyst; contacting theMTBE with the hydrofluoric acid-treated synthetic alumina-silicacatalyst under decomposition conditions to produce a reactor effluentcomprising isobutylene, unreacted MTBE, heavies, and methanol; feedingthe reactor effluent to a first distillation column; separating theisobutylene from the unreacted MTBE, heavies, and the methanol in thefirst distillation column to recover a first bottoms fraction comprisingheavies, unreacted MTBE, and methanol and an isobutylene-rich overheadsfraction.

In another aspect, embodiments disclosed herein relate to a catalystuseful for the decomposition of ethers and alcohols to form olefins, thecatalyst comprising a hydrofluoric acid-treated amorphous syntheticalumina-silica catalyst.

In another aspect, embodiments disclosed herein relate to a process forthe production of olefins from at least one of an alcohol and an ether,the process comprising: contacting at least one of an alcohol and anether with a selectively poisoned amorphous synthetic alumina-silicacatalyst under decomposition conditions to produce an olefin.

Other aspects and advantages will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified process flow diagram for producing tertiaryolefins according to embodiments disclosed herein.

FIG. 2 is a graphical comparison of the catalyst activity, as measuredby MTBE conversion, of catalysts according to embodiments disclosedherein as compared to prior art catalysts.

FIG. 3 is a graphical comparison of the catalyst activity, as measuredby MTBE conversion, of catalysts according to embodiments disclosedherein as compared to prior art catalysts.

FIG. 4 is a simplified process flow diagram for producing tertiaryolefins according to embodiments disclosed herein.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to a process for theproduction of olefins from ethers and alcohols, and catalysts therefore.In another aspect, embodiments disclosed herein relate to a process forthe production of catalysts useful for the cracking of ethers andalcohols to form olefins.

Catalysts useful in embodiments disclosed herein include amorphoussynthetic alumina-silica catalysts. In some embodiments, catalystsuseful in embodiments disclosed herein include hydrofluoric acid (HF)treated amorphous synthetic alumina-silica catalysts. Amorphoussynthetic alumina-silica catalysts may be prepared by co-precipitationor impregnation techniques, followed by drying and calcination. Theamorphous alumina-silica materials may contain from about 0.1 to about99 weight percent silica in some embodiments; from about 1 to about 98weight percent silica in other embodiments; from about 2 to about 98weight percent silica in other embodiments; from about 2 to about 97weight percent silica in other embodiments; and from about 3 to about 96weight percent silica in yet other embodiments. Although describedherein as amorphous, alumina-silica materials useful in embodimentsdescribed herein may contain a minor amount of crystalline alumina,depending on the source of the alumina material used to prepare theprecipitated alumina-silica precursor, the amount of the alumina in thealumina-silica, as well as the calcination temperature.

The catalysts may also contain one or more optional elements, includingtitanium, zirconium, hafnium, tantalum, and niobium, in an amount fromabout 0 weight percent up to about 10 weight percent; from about 0.01weight percent to about 3 weight percent in other embodiments. Theseoptional elements may be incorporated into the catalyst material priorto HF treatment or introduced to the material after HF treatment.

The HF treated amorphous synthetic alumina silica catalysts useful inembodiments disclosed herein may be prepared by treating amorphoussynthetic alumina-silica with a dilute aqueous HF solution at ambienttemperature. The amount of HF required for the treatment depends on thedetailed composition of a given amorphous synthetic alumina and itsphysical properties. In general, the amount of anhydrous hydrofluoricacid used during the treating step may range from greater than 0 g toabout 65 g per kg of alumina-silica. For dilute HF solutions, such as a50% HF solution, the amount of dilute HF should be adjusted accordingly;for the 50% HF, for example, the amount of 50% HF solution may rangefrom greater than 0 g to about 130 g per kg of alumina-silica. In otherembodiments, the amount of anhydrous hydrofluoric acid used during thetreating step may range from about 10 g to about 40 g per kg ofalumina-silica (20 g to 80 g per kg alumina-silica for a 50% HFsolution). HF solutions, used at the above ratios, may be diluted withadditional water so as to completely immerse the entire volume ofalumina-silica to be treated in dilute HF.

It is additionally noted that the above ratio of HF to amorphousalumina-silica is significantly less than the ratio of HF to attapulgiteclay typically used in forming HF treated attapulgite clays, asdescribed above. Thus, the HF treated amorphous synthetic alumina-silicacatalysts described herein may be environmentally more disposable.Additionally, less fluorinated waste solution may be generated. Each ofthese may contribute to a decrease in raw material and disposal costsfor catalyst manufacture.

The amorphous alumina-silica may be contacted with the diluted HFsolution for a time ranging from 5 minute to 2 hours in someembodiments; from 15 minutes to 90 minutes in other embodiments. Thetreating may be performed at a temperature from room temperature toabout 90° C., and the slurry may be stirred continuously orintermittently. The HF treatment of amorphous synthetic alumina-silicacatalysts may be performed in a single step or multiple steps.

Following HF treatment, the excess solution in the treatment vesselshould be drained, and the HF treated amorphous synthetic alumina-silicamay be washed with sufficient amounts of clean, deionized water. Thecatalyst may then be dried and calcined prior to use as a catalyticmaterial. Calcining may be performed at a temperature from 300° C. to850° C. in some embodiments; at a temperature ranging from 400° C. to750° C. in other embodiments.

Amorphous synthetic alumina-silica catalysts and HF treated amorphoussynthetic alumina-silica catalysts according to embodiments disclosedherein may have a high activity, which may result in the production ofundesired byproducts, such as isoalkanes and ethers. Isoalkanebyproducts may undesirably complicate product purification/separationsas the boiling points of the isoalkanes are similar to that of thetertiary olefins. Additionally, while HF treatment may result incatalysts having a higher activity and longer cycle times than untreatedamorphous synthetic alumina-silica catalysts, polymer deposition andbyproduct production may remain problematic.

Selective poisoning of strongly acid sites on both amorphous syntheticalumina-silica catalysts and HF treated amorphous syntheticalumina-silica catalysts may improve catalyst selectivity, reducing bothproduction of unwanted byproducts and formation of polymers, thusfurther resulting in extended catalyst cycle times. Selective poisoningand related terms (selectively poisoned, etc.) as used herein refers tothe treatment of the catalyst to neutralize (poison) unwanted acid sitesin the catalyst structure having a high acidity or sites ofunnecessarily too strong acid strength. The selectively poisonedcatalysts disclosed herein may thus have a moderate acidity or mildacidity or both, in general terms, as a whole, as the acid sites havinga comparatively high acidity and/or unwanted sites are selectivelypoisoned.

Selective poisoning of catalysts disclosed herein may be performed bytreating the catalysts with one or more compounds that may react orinteract with strong acidic sites and/or unwanted catalytic sites withinthe catalyst. Examples of compounds useful for selective poisoning mayinclude alkali metal compounds, alkaline earth compounds, bismuthcompounds, and other basic compounds known to those skilled in the art.Such compounds may include elements, which are effective for selectivepoisoning, including Na, K, Rb, Cs, Mg, Ca, Cu, Pb, Cr. Be, Sn, Sr, Ba,Zn, Fe, Ti, Bi, Mo, Mn, La, Ce, and Ac, among others.

The amount of the selective poisoning element or elements contacted withand reacted onto the amorphous synthetic alumina-silica may depend onthe nature of intended reaction (or specific reactant), specificcatalyst compositions, and the specific element used for poisoning. Theamount of metal elements on a catalyst for selective poisoning may bewithin the range from about 5 ppm to about 8% by weight in someembodiments; from about 10 ppm to about 4% by weight in otherembodiments. In various embodiments, the compounds used for treating acatalyst can be either an inorganic or organic salt or organometalliccompound metal hydroxide. The poisoning may be performed in aqueousmedium, organic medium or a mixed medium of water and an organicsolvent.

To selectively poison amorphous synthetic alumina-silica catalystsaccording to embodiments disclosed herein, the catalyst may be treatedwith an aqueous or organic solution of a compound or compounds usefulfor selectively poisoning at a temperature in the range from about 0° C.to about 200° C. in some embodiments; at a temperature from about 10° C.to about 125° C. in other embodiments. The treating method can be anymethod as long as it produces the intended result, namely the selectivepoisoning of highly acidic and/or unwanted sites, examples of whichinclude ion-exchange methods, impregnation, soaking, refluxing, etc.After contact with the selective poisoning compound or compounds, theselectively poisoned catalyst may be washed with a solvent, such aswater, alcohol, acetone, or a mixture thereof, and dried. After drying,the catalyst may be calcined at a temperature in the range from about150° C. to about 800° C. in some embodiments, from about 200° C. toabout 600° C. in other embodiments, for a period of time in the rangefrom about 5 minutes to about 24 hours, such as from about 15 minutes toabout 6 hours.

Alternatively, selective poisoning of the catalyst may be performed insitu. For example, a small amount of a basic compound may be added intothe decomposition reactor with a feed stream. The basic compound addedmay be non-reactive with the hydrocarbons present under reactioncondition and should not interfere with the separation and recovery ofthe desired reaction products (i.e., selectively poisoning the catalystwhile not interfering with the desired hydrocarbon processing). Examplesof basic compounds that may be added for poisoning of the catalyst insitu may include ammonia and dimethyl ether, among others.

The above described HF treated amorphous synthetic alumina-silicacatalysts, selectively poisoned amorphous synthetic alumina-silicacatalysts, and selectively poisoned HF treated amorphous syntheticalumina-silica catalysts may be used to produce various olefins fromethers and alcohols. Various olefins which may be obtained according toprocesses described herein include ethylene, propylene, isobutylene,isoamylenes such as 2-methyl-2-butene and 2-methyl-1-butene, isohexenes,such as 2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene,2-methyl-1-pentene, 2-methyl-2-pentene, (cis and trans)3-methyl-2-pentene, 2-ethyl-1-butene and 1-methyl-cyclopentene, and thetertiary isoheptenes. Such olefins may be produced from suitable alkyltertiary-alkyl ethers, tertiary alcohols, sec-alkyl ethers, primaryalcohols, and mixtures thereof. For example, isobutylene may be producedby decomposing one or more of MTBE, ethyl tertiary-butyl ether (ETBE),and tertiary butyl alcohol (TBA). Isoamylene may be produced bydecomposing TAME or tertiary-amyl ethyl ether (TAEE). Propylene may beproduced by decomposing diisopropyl ether (DIPE), isopropyl alcohol(IPA), or mixtures thereof. In other embodiments, secondary alcohols mayalso be used.

As further examples, ethylene may be produced by dehydrating ethanol ora mixture of ethanol and diethyl ether. So-called “renewable ethylene”may be produced by dehydrating bio-ethanol. Additionally, diethyl ethermay be produced by dehydrating ethanol. The diethyl ether by-product maybe recovered from the reactor effluent stream and recycled as part ofthe feed mixture. Catalysts described above may also be used for thedehydration of methanol to produce dimethyl ether (DME), which may beused in or as diesel fuels.

Catalysts and processes described herein are also useful in theproduction of high purity isobutylene by decomposing MTBE, TBA, ormixtures thereof. Decomposing a mixture of MTBE with a minor amount ofTBA to produce isobutylene may be preferred over MTBE alone as lessundesirable by-products, such as isobutane, DME, and diisobutylene, areproduced.

Optionally, a small amount of water or water equivalents may be addedwith the feed to suppress unwanted side reactions. As used herein,“water equivalents” refers to water added to the reactor directly or towater added to the reactor indirectly, such as by decomposition of analcohol to form water and an olefin, where the alcohol may be used in anamount sufficient to result in an equivalent amount of water in thereactor. For example, in the alternative to adding water to the feedwhen decomposing MTBE, feed of TBA to the reactor, and the subsequentdecomposition of the TBA, will produce a similar olefin, isobutylene,with the co-production of water. The amount of water equivalents used invarious embodiments may range from 0.1 to 5 weight percent; up to 3weight percent water in other embodiments, up to 1.0 weight percent inother embodiments, where the above values are based on the total weightof water equivalents and the ether feed.

Addition of water or TBA to an MTBE feed stream, for example, may bebeneficial during the early stage of MTBE decomposition to suppressunwanted side reactions. As the catalyst slowly deactivates, the amountof water or TBA addition may be slowly reduced.

The cracking reaction (also referred to herein as decomposition ordehydration) may be performed in one or more fixed bed reactors in thepresence of a catalyst disclosed in this invention such as an HF treatedamorphous synthetic alumina-silica catalyst as described above. Examplesof fixed bed reactors useful in embodiments disclosed herein may includetubular reactors, boiling point reactors, bubble column reactors,traditional fixed bed reactors, catalytic distillation columns, dividedwall distillation column reactors, pulsed flow reactors, andcombinations thereof. One or more of such reactors may be used inparallel flow or series flow.

Decomposition reaction conditions may vary based on the feed mixtureused and the desired olefins produced. Decomposition temperatures mayrange from 100° C. to 500° C. in some embodiments; from 130 to 350° C.in other embodiments and from 150° C. to 300° C. in yet otherembodiments. The decomposition reaction may be carried out underpressures in the range from 1 to 22 bar (0 to 300 psig) in someembodiments; from 1 to 11 bar (0 to 150 psig) in other embodiments. Insome embodiments, the pressure is maintained such that the productolefin is in the liquid phase or partially in the liquid phase at thereaction temperature used. The liquid hourly space velocity (LHSV) (thevolume of liquid per volume of catalyst per hour) at which the reactionis carried out may be within the range from 0.5 to 200 h⁻¹ in someembodiments; from 1 to 50 h⁻¹ in other embodiments; and from 1 to 10 h⁻¹in yet other embodiments.

Contact of the alcohol and/or ether feed with catalysts as describedherein, at decomposition conditions, may result in the production of thedesired olefin, alcohols, and heavies, which may include by-productethers, alcohols, and oligomers, such as a dimer or trimer of thedesired olefin product. In some embodiments, contact of an ether feedwith catalysts as described herein may result in conversion of at least90 weight percent of the ether; at least 85 weight percent in otherembodiments; at least 80 weight percent in other embodiments; at least75 weight percent in other embodiments; and at least 70 weight percentin other embodiments.

Catalysts disclosed herein may maintain their catalytic activity for anextended service life. For example, catalysts disclosed herein maymaintain a conversion of at least 65 weight percent of an ether feed forat least 9 months in some embodiments; at least 1 year in otherembodiments; at least 15 months in other embodiments; at least 18 monthsin other embodiments; and up to 2 years or more in yet otherembodiments.

Catalysts and processes disclosed herein may be used to produce andrecover a high purity olefin product stream. For example, in someembodiments, a desired olefin may be recovered in an olefin-rich stream(as used herein, a stream rich in a particular component comprises atleast 50 weight percent of said component). In other embodiments, therecovered olefin-rich fraction may have an olefin content greater than90 weight percent; greater than 95 weight percent in other embodiments;greater than 97 weight percent in other embodiments; greater than 98weight percent in other embodiments; greater than 98.5 weight percent inother embodiments; greater than 99 weight percent in other embodiments;greater than 99.1 weight percent in other embodiments; and greater than99.5 weight percent in yet other embodiments. In other embodiments, theolefins recovered may be useful as a polymerization feedstock, having apurity of at least 99.8 weight percent.

Referring now to FIG. 1, a simplified process flow diagram for theproduction of isobutylene from MTBE using the catalysts described hereinis illustrated. Similar flow schemes may be used for the production ofother olefins from feed stocks as described above, and will not bedetailed herein.

MTBE feed 10 and optional water or TBA feed 12 are introduced to a fixedbed decomposition reactor 14. Decomposition reactor 14 may include oneor more beds 16 of an HF treated amorphous alumina-silica catalysts asdescribed herein. The MTBE may be contacted with the HF treatedamorphous alumina-silica catalyst under decomposition conditions toproduce a reactor effluent 18, which may include one or more ofunreacted MTBE, heavies (such as diisobutylene and other heavieroligomers and by-products), methanol, and the desired product,isobutylene.

Reactor effluent 18 may be fed to a first distillation column 20 toseparate and recover the isobutylene. The isobutylene may be separatedfrom unreacted MTBE, methanol, and heavies, recovering anisobutylene-rich overhead fraction via flow line 22. Isobutylene-richoverheads, in some embodiments, may be a high purity isobutylene stream,having a concentration of at least 99.5 weight percent isobutylene.

The unreacted MTBE, methanol, and heavies may be recovered as a bottomsfraction from distillation column 20 and fed via flow line 24 to asecond distillation column 26, where the unreacted MTBE may be separatedfrom the heavies and the methanol. The unreacted MTBE may be recoveredas an MTBE-rich overheads fraction via flow line 28, a portion of whichmay be recycled via flow line 30 to reactor 14 in some embodiments.

The heavies and methanol may be recovered as a bottoms fraction fromdistillation column 26 via flow line 32. If desired, the methanol may berecovered from the heavies, such as by feeding the heavies and methanolin flow line 32 to third distillation column 34. A methanol-richoverheads fraction may be recovered via flow line 36 and a heavies-richbottoms fraction may be recovered via flow line 38.

As mentioned above, similar flow schemes to that presented in FIG. 1 maybe used for the production of other olefins from feed stocks asdescribed above. For example, additional reactors may be used, oradditional separations may be required where the feed includes a mixtureof ethers and/or alcohols resulting in the production of more than onedesired olefin.

It is further noted that various schemes to recycle and reuse variousreaction by-products may be used, promoting the overall conversion ofthe feed to the desired olefin. For example, diethyl ether produced as aby-product from the dehydration of ethanol may be recovered from thereactor effluent stream and recycled as part of the feed mixture.

The type of reactors for the decomposition of ethers and alcohols toolefins or for the dehydration of alcohols to ethers according toembodiments disclosed herein is not limited to any particular physicaldevice. Any decomposition and dehydration reaction in the presence ofthe catalysts disclosed herein can be carried out in any physicaldevice. Examples of suitable reactors for the decomposition of ethersand alcohols, and dehydration of alcohols to ethers may includetraditional fixed bed tubular reactors, distillation column reactors,boiling point pulse flow reactors, and divided wall distillation columnreactors, among others.

The reactions may be carried out in the vapor phase, liquid phase, ordual phase of liquid and vapor. Because of the equilibrium nature of thereactions, carrying out the reactions in the vapor phase or dual phaseof vapor and liquid may result in a higher conversion per pass or higherolefin productivity than a liquid phase reaction, which may also requirehigher pressure.

In some embodiments, olefins may be produced according to embodimentsdisclosed herein by carrying out the reactions in a catalytic dividedwall distillation column, such as illustrated in FIG. 4. FIG. 4illustrates a simplified process flow diagram for the catalyticdecomposition of MTBE by using a divided wall distillation column. MTBEfeed 41 is introduced to a proper position above catalytic reaction zone44 in a catalytic divided wall distillation column 40 via line 43. Asmall stream 42 of water or TBA is also introduced to the column 40above the catalyst zone 44. The decomposition product isobutylene isremoved from the column 40 as overhead steam 45 along with minor amountsof by-products, including DME and isobutane. The isobutylene in stream45 may be recovered as better than 99.5% purity product, as describedabove, by use of various separation schemes, such as distillation (notshown). The unreacted MTBE may be recovered by a side-draw stream 46from the column 40 and recycled back via line 43. The bottom stream 47from the column 40 includes methanol, water and heavies, and may beintroduced to a distillation column 48 to recover methanol as overheadstream 49. The bottom stream 50, including the heavies and water, may betreated and disposed.

EXAMPLES

All MTBE decomposition reactions in the following Examples are carriedout in a down flow reactor having a fixed bed of catalyst ½ inches indiameter and 21 inches long. The reactor has top and bottom heatingzones, which are separately controlled. The fixed bed reactor is mountedvertically. The volume of solid catalysts tested was approximately 15 mlfor each.

Comparative Example 1

A granular attapulgite clay (16 to 30 mesh) is calcined at 500° C. for 2hours. This calcination is necessary to maintain physical integrity ofthe clay granules during aqueous hydrofluoric acid (HF) treatment.

A fluorinated attapulgite clay catalyst is prepared according to theprocedure disclosed in U.S. Pat. No. 4,691,073. 34.2 grams calcinedattapulgite clay granules is treated in an aqueous HF solution preparedby diluting 6.95 grams of 50% HF with 61.5 grams deionized water atambient temperature for 1 hour with occasional stirring. After decantingout the excess solution, the clay is washed twice with 80 ml deionizedwater. The wet clay is dried at 100° C. in a vacuum oven for 1 hour andthen calcined at 500° C. for 2 hours. This calcined catalyst is referredto herein as “F-ATT-1.”The physical properties of the resulting catalystare 151 m²/g BET; 0.386 cc/g total nitrogen adsorption/desorption porevolume; and an average pore diameter of 10.2 nm.

15 ml of F-ATT-1 catalyst is loaded in the reactor described above andtested with a crude mixed MTBE feed stock containing 95.9 wt. % MTBE.The feed also contains small amounts of highly unsaturated compoundssuch as 1,3-butadiene, trans-1,3-pentadiene, cis-1,3-pentadiene,2-methyl-1,3-butadiene, and others. The test condition is 31 psig, 290°F., and 2.0 liquid hourly space velocity (LHSV) feed down-flow rate. Theresult of the test is illustrated in FIG. 2.

Comparative Example 2

A alumina-silica catalyst is prepared by co-precipitation method. Thedried alumina-silica powder is extruded to 3 mm pellets, which arecalcined at about 500° C. for 2 hours. The pellets are ground to 12-14mesh granules. The granular alumina-silica catalyst contained 20%silica. This catalyst is referred to herein as “KL7122.” The physicalproperties of the catalyst are 379.2 m²/g BET; 0.646 cc/g total nitrogenadsorption/desorption pore volume; and an average pore diameter of 6.89nm.

15 ml of KL7122 catalyst is tested under identical conditions as givenfor Comparative Example 1, with the same reactor and feed. The result isillustrated in FIG. 2.

The performances of the two catalysts in Comparative Examples 1 and 2are very similar. Both catalyst F-ATT-1 and KL7122 have an initialactivity of about 85% conversion of MTBE, but they deactivate rapidly.After only about 80 hours on stream, the MTBE conversion was only about20%.

Experiment 3

25.7 grams of the alumina-silica granules described in ComparativeExperiment 2 are treated with an aqueous HF solution prepared bydiluting 2.79 grams of 50% HF with 47.75 grams deionized water atambient temperature for 1 hour with occasional stirring. The amount ofHF used is approximately only 53.4% of that used in ComparativeExample 1. After decanting out the excess solution, the alumina-silicagranules are washed four times with 60 ml deionized water. After dryingat 100° C. in a vacuum oven for 1 hour, the granules are calcined at500° C. for 2 hours. This HF-treated amorphous silica alumina catalystis referred to herein as “F-KL7122-1.”

15 ml of F-KL7122-1 catalyst is tested in an identical manner toComparative Example 1. The result is also illustrated in FIG. 2.

The initial activity of this catalyst is similar to the catalysts ofComparative Examples 1 and 2 (F-ATT-1 and KL7122). However, as shown inFIG. 2, the performance of this HF treated alumina-silica catalyst issuperior to the comparative catalysts (F-ATT-1 and KL7122). It takesapproximately twice the service time to reach the same degree ofdeactivation. Therefore, the fluorinated alumina-silica is an improvedcatalyst for decomposition of ethers such as MTBE.

Comparative Example 4

Another granular attapulgite clay (16-30 mesh) is calcined at 500° C.for 2 hours. A fluorinated attapulgite clay catalyst is prepared in asimilar manner to Comparative Example 1. 32.2 grams calcined attapulgiteclay granules is treated in an aqueous HF solution prepared by diluting6.54 grams of 50% HF with 62.0 grams deionized water at ambienttemperature for 1 hour with occasional stirring. After decanting out theexcess solution, the clay is washed three times with 70 ml deionizedwater. The wet clay is dried at 100° C. in a vacuum oven for 1 hour andthen calcined at 500° C. for 2 hours. This calcined catalyst is referredto herein as “F-ATT-2.”

A high purity MTBE (99.69 wt. %) feed is decomposed over catalystF-ATT-2. This MTBE feed contains no highly unsaturated compounds. Thedecomposition is carried out under similar conditions (31 psig, 290° F.,2.0 LHSV feed down-flow rate) as Comparative Example 1. The result ofthe decomposition is illustrated in FIG. 3.

The initial catalyst activity is about 90% MTBE conversion. The catalystactivity is much more stable compared with the F-ATT-1 catalyst ofComparative Example 1. Nevertheless, the experimental result predictszero catalytic activity after about 1500 hours on stream. Commercially,the goal for MTBE conversion is typically about 65%, and the catalystactivity decreases below this conversion goal in about 400 hours.

Experiment 5

A fluorinated amorphous alumina-silica catalyst is prepared in a mannersimilar to Experiment 3, with a reduced quantity of HF. 26.92 grams ofthe alumina-silica granules described in Comparative Experiment 2 aretreated with an aqueous HF solution prepared by diluting 2.02 grams of50% HF with 47.18 grams deionized water at ambient temperature for 1.5hours with occasional stirring. The amount of HF used is approximatelyonly 37% of that used in Comparative Example 1. After decanting out theexcess solution, the alumina-silica granules are washed four times with60 ml deionized water. After drying at 100° C. in a vacuum oven for 1hour, the granules are calcined at 500° C. for 2 hours. This HF-treatedamorphous silica alumina catalyst is referred to herein as “F-KL7122-2.”The physical properties of the catalyst are 312.0 m²/g BET; 0.635 cc/gtotal nitrogen adsorption/desorption pore volume; and an average porediameter of 8.15 nm.

15 ml of F-KL7122-2 catalyst is tested with the high purity MTBE used inComparative Example 4. The initial start-up condition is 65 psig, 284°F. and 2.0 LHSV. Operating conditions were adjusted during the run asnoted in the results as shown in FIG. 3.

The performance of this HF treated alumina-silica catalyst is superiorto that of the clay catalyst in Comparative Example 4. There is littleor no catalyst deactivation during the entire run (1659 hours). Theprojected life of this catalyst is at least one year or longer.

It is additionally noted that the HF treated alumina-silica catalystsdescribed in Experiments 3 and 5, as compared to the clay catalysts, maybe regenerated by calcining at a temperature in the range of 400° F. to600° F. in air. The regenerability of the HF treated amorphous syntheticalumina-silica catalysts described herein may decrease the amount ofwaste produced due to catalyst replacement, among other advantages.

As described above, hydrofluoric acid treated amorphous syntheticalumina-silica catalysts as described herein may be useful for thedecomposition of alcohols and ethers to form olefins. In a family ofembodiments, the hydrofluoric acid treated amorphous syntheticalumina-silica catalysts as described herein may be useful for thedecomposition of alkyl tertiary-alkyl ethers to form tertiary olefins,such as isobutylene, isoamylenes, and others.

Advantageously, embodiments disclosed herein may provide for a catalystuseful for decomposition reactions having an extended cycle length,deactivating over a period of up to 2 years or more in some embodiments.The extended service life may result in decreased olefin productioncosts, including decreased catalyst cost as well as decreased catalystdisposal costs. Additionally, embodiments of the catalysts describedherein may have one or more of good physical integrity, a low attritionrate, and a high crushing strength. Further, manufacture of thecatalysts described herein may use significantly decreased quantities ofraw materials, such as hydrofluoric acid, as compared to prior artcatalysts, thus reducing catalyst production and raw material disposalcosts.

While the disclosure includes a limited number of embodiments, thoseskilled in the art, having benefit of this disclosure, will appreciatethat other embodiments may be devised which do not depart from the scopeof the present disclosure. Accordingly, the scope should be limited onlyby the attached claims.

What is claimed:
 1. A catalyst useful for the decomposition of ethersand alcohols to form olefins, the catalyst comprising a selectivelypoisoned amorphous synthetic alumina-silica catalyst; wherein theamorphous synthetic alumina-silica catalyst is prepared by a processcomprising: contacting the amorphous synthetic alumina-silica catalystwith a poison at a temperature from 0° C. to 200° C.; washing theselectively poisoned amorphous synthetic alumina-silica catalyst with asolvent comprising water, alcohol, acetone, or a mixture thereof; dryingthe washed selectively poisoned amorphous synthetic alumina-silicacatalyst; calcining the dried selectively poisoned amorphous syntheticalumina-silica catalyst at a temperature from 200° C. to 600° C.; andwherein selective poisoning elements are selected from the groupconsisting of Na, K, Rb, Cs, Cu, Pb, Cr, Sn, Zn, Ti, Bi, Mo, La, Ce, andAc.
 2. The catalyst of claim 1, wherein the amorphous syntheticalumina-silica catalyst comprises from 2 to 98 weight percent silica. 3.The catalyst of claim 1, further comprising up to 10 weight percent ofat least one of Ti, Zr, Hf, Ta, and Nb.
 4. A catalyst useful for thedecomposition of ethers and alcohols to form olefins, the catalystcomprising a hydrofluoric acid-treated amorphous syntheticalumina-silica catalyst; wherein the catalyst is produced by a processcomprising: contacting an amorphous synthetic alumina-silica with adilute hydrofluoric acid solution, wherein a ratio of hydrofluoric acidto alumina-silica during the contacting is in the range from greaterthan 0 g to about 65 g hydrofluoric acid per kg of alumina-silica;separating the dilute hydrofluoric acid solution from the catalyst;washing the catalyst to remove excess hydrofluoric acid; and calciningthe catalyst at a temperature in the range of 300° C. to 850° C.
 5. Acatalyst useful for the decomposition of ethers and alcohols to formolefins, the catalyst comprising an amorphous synthetic alumina-silicacatalyst selectively poisoned with one or more elements selected fromthe group consisting of Na, K, Rb, Cs, Cu, Pb, Cr, Sn, Zn, Ti, Bi, Mo,La, Ce, and Ac.
 6. The catalyst of claim 5, wherein the amorphousalumina-silica catalyst comprises from 2 to 98 weight percent silica. 7.The catalyst of claim 5, further comprising up to 10 weight percent ofat least one of Ti, Zr, Hf, Ta, and Nb.
 8. The catalyst of claim 5,wherein the catalyst is produced by a process comprising: contacting anamorphous synthetic alumina-silica with a selective poisoning compoundunder conditions to react an acid site on the amorphous syntheticalumina-silica catalyst with the selective poisoning compound to producethe selectively poisoned amorphous synthetic alumina-silica catalyst.